This is a known problem in the current version of the vBulletin Sphinx Search by Digital Point.
There is a fix, but unfortunately it will cost us at least $25.00 to be able to download the latest version of the software and we just can't spare the money right now.
I don't think I'm dealing with quite the same pressures though, at the very least its a significantly smaller system. For the time being I'm just going to put together a quick scrubby box though and hope it works good enough to not make my house toxic
I do know this - xenforo dropped the ball by not keeping the vbulletin reputation comments as a feature. The loss of the Reputation comments data when we switched to Xenforo really was the death knell for the site when it came to all the users that left. I know I missed it so much and I got way less interested in the site when that feature was gone and I run the site.